Various methods and devices exist for determining the relative position of a person or an object, with accuracies varying widely depending on the particular technology that is utilized. For example, a global positioning system (GPS) receiver embedded or contained within a portable or vehicle-mounted navigation system allows a user to receive satellite-transmitted positional information. Depending on the number of GPS signal transmitting satellites positioned within line of sight of the receiver at a given moment, the positional information can vary in both relative accuracy and specificity. That is, using GPS capabilities, 2-dimensional (2D) information, i.e., the present latitude and longitude of the user, or 3D positional information, i.e., the user's latitude, longitude, and altitude, can be provided within a fair degree of accuracy, in some cases as low as approximately +/−3 meters of their true position.
By way of contrast, a local positioning system (LPS) can be used to provide more precise positional information. For example, by using an LPS device or devices in a large manufacturing facility one can identify a particular area or zone of the facility in which a pallet of supplies or inventory is located, or a loading dock on which a shipment awaits shipping or receiving. A few of the more common LPS technologies include optical detection devices, infrared systems, ultra-wide band detection, and radio frequency identification (RFID) tagging, with each technology having its own advantages and disadvantages. For example, while RFID tagging is useful for certain purposes such as securely tagging a piece of merchandise to minimize theft, such a device has a limited effective distance and accuracy. Likewise, optical systems and infrared systems can perform in a less than optimal manner when used in certain high-precision applications, due in part to the potential interference provided by the many obstructions encountered in a modern work space, e.g., metallic structures and/or proximate heat sources.
In a high-volume manufacturing assembly environment, certain steps in the assembly process can be automated to minimize cost and increase production throughput and accuracy. Assembly robots having an associated hard-wired data encoder for each axis of movement can rapidly perform traditionally labor intensive assembly steps such as fastening, welding, painting, etc. However, when a work piece is positioned in a relatively restricted or confined work space, the use of an automated assembly robot may not be efficient, or even feasible. In such cases, an operator having a handheld assembly tool can enter the confined work space to perform the required assembly steps, such as is commonly experienced in certain automotive assembly processes. The conventional global and local positioning devices and methods described above can be less than optimal in such applications, particularly when the positioning devices are used for measuring the often incremental positional changes of the assembly tool as it moves between assembly positions within the confined work space.